EFFECT OF CALCIUM SALTS OF FATTY-ACIDS ON RUMEN FUNCTION AND THE DIGESTIBILITY OF RATIONS BY SHEEP

Experiments were conducted to determine the effects of supplementing c hopped ryegrass hay with 0, 1.5, 3, 6 or 12% calcium salts of fatty ac ids (CaSFA; Megalac (R)) on digestion in the rumen of cannulated cows and on nutrient digestibility by sheep. In-situ ruminal disappearances of dry matter (DM) and cell wall fractions (acid detergent fibre, ADF , and neutral detergent fibre, NDF) were measured by the nylon bag tec hnique. The DM, ADF and NDF disappearances were reduced for diets cont aining CaSFA at the 1.5, 3 or 6% levels after 48 h of rumen exposure. For diets containing 12% CaSFA, irrespective of the time of rumen incu bation, DM disappearance was decreased, while ADF and NDF breakdown wa s improved. CaSFA supplementation did not influence in vitro fermentat ion characteristics (pH, volatile fatty acid patterns). A digestibilit y experiment with six mature sheep showed no difference in nitrogen di gestibility between unsupplemented and CaSFA-supplemented diets. Howev er, digestibilities of DM, ADF and NDF were higher relative to the bas al for the 12% CaSFA: 63.1 versus 60.6%, 63.8 versus 58.7% and 67.4 ve rsus 62.7%, respectively. Ether extract digestion was enhanced by incr easing the level of CaSFA, the corresponding values being 49.1, 66.5, 78.6, 81.9 and 77.9% at 0, 1.5, 3, 6 and 12% CaSFA, respectively. Appa rent digestibility of energy was higher for the 12% CaSFA than the con trol diet (68.8 versus 62.1%). Nitrogen and energy retention was impro ved due to the decreases in urine and faecal excretion, respectively.